In a conventional impulse coil tester, the same impulse voltage is simultaneously impressed on a reference master coil and on a coil under test and damped oscillation current waveforms flowing through the respective coils are comparatively observed on a cathode-ray tube to judge the quality of the coil under test.
FIG. 5 is a block connection diagram of such a conventional impulse coil tester. In the diagram, the reference numeral 1 represents a sweep circuit having a sweep oscillator, 2 represents a cathode-ray tube into whose horizontal deflecting plate are input saw tooth waves from the sweep oscillator and 3 represents a voltage regulator generating a high voltage to be input into a rectifier 4. A charging and discharging capacitor 5 is connected to this rectifier 4. A thyristor 8, functioning to input a high voltage with which the capacitor 5 is to be charged into voltage dividing capacitor 6 and 7 at a fixed timing, is connected to this capacitor 5. A trigger signal is input into the gate of this thyristor 8 at a fixed timing from a trigger circuit 9. The reference numerals 10 and 11 represent respectively a coil under test and a master coil which are connected to the thyristor through a relay switch 12. Reference numerals 13 and 14 represent current detecting resistances. The reference numeral 15 represents a comparator for comparing the damped oscillation current waveforms of the coil under test 10 and master coil 11 to judge the quality of the coil under test and 16 represents a sensitivity regulating resistor. An indicator such as a light emitting diode is connected to the comparator to judge and indicate the quality of the coil under text.
However, in such a conventional impulse coil tester, there have been problems that the master coil is always required to measure the characteristics of the coil under test 10 and a high voltage impulse is so often repeatedly impressed on the master coil so that the measuring error becomes large while the deterioration is not noticed. This results in a failure to correctly measure the characteristics of the coil under test. Additionally, as only the voltage and current flowing through both coils 10 and 11 are compared in measuring the quality with the comparator 15, the error appearing when the damping of the current flowing while oscillation has progressed and the oscillation amplitude has become small is hard to detect. That is to say, it has not been possible to judge the above-mentioned error by discriminating the frequency and amplitude size of the output waveform.